The invention relates to a method of manufacturing a mercury vapor discharge lamp, having a lamp vessel provided with an exhaust tube, the quantity of mercury required for the operation of the lamp being present in metallic form in a closed metal container, and more particularly to such a lamp whose container is mainly shaped as a plate arranged in the exhaust tube and held in place by a waist portion of the plate engaging and a rib in the exhaust tube. The container is heated after evacuation of the lamp in a manner such that it opens due to the mercury vapor pressure building up therein. The invention further relates to a lamp manufactured by means of this method and to a container filled with metallic mercury and suitable for carrying out the method as well as to a lamp vessel in which such a closed container filled with mercury is present.
A method of the aforementioned kind is known from British Patent Specification No. 1,475,458. In this Patent Specification, a method of manufacturing a mercury vapor discharge lamp (such as, for example, a low-pressure mercury vapor discharge lamp having a tubular lamp vessel) is described, in which first a closed metal container is arranged in the exhaust tube. The container comprises a first portion containing the mercury and a second, larger portion having the form of a lamina. After substantially all the manufacturing steps relating to the evacuation process (such as degasing the wall and the remaining lamp parts, annealing and degasing the electrodes, providing the rare gas etc.) have been accomplished, the lamp vessel is sealed in a gas-tight manner and the container is heated, for example, by means of a high-frequency electric field. Due to this heating, mercury is released from the holder and moves into the lamp vessel.
Due to the use of a container which is plate-shaped for the major part, and a correct arrangement thereof in the exhaust tube, the flow resistance during the evacuation process is increased to the least possible extent. The container is therefore preferably arranged so that it extends in the longitudinal direction of the exhaust tube. The known container comprises, for example, a flat plate with a small cup which is welded thereto and which contains the mercury.
In the known method, the container is arranged in the exhaust tube by pushing the plate-shaped part of the container in the exhaust tube through the rib until it reaches a position in which the reduced-width portion in the container cooperates with the rib in the exhaust tube. In order to prevent that so much force has to be excerted on the container during this step, that the exhaust tube is damaged, which may even lead to rupture, according to the aforementioned Patent Specification, a slot is provided in the longitudinal direction in the plate-shaped part of the container. The resilient properties are then improved and the plate-shaped part of the container can pass the rib more easily. Moreover, a larger tolerance in the dimensions of the narrow passage at the area of the rib in the exhaust tube is permissible.
It has been found that very strigent requirements have to be imposed on the correct length of the slot. If the slot is too short, the resilient properties are insufficient and there is a risk that during the step of providing the container rupture of the exhaust tube will nevertheless occur. If on the contrary the slot extends over too large a part of the container, the plate-shaped parts located on either side of the slot can be readily deformed when the incision is provided. Such a deformation has the disadvantage that during the sorting and selection step (which precedes the step of providing in the exhaust tube) adjacent containers are liable to hook one into the other, as a result of which disturbances occur. This is disadvantageous especially in a mass-production process.